SoCalGas says it discovered the gas leak on 23 October at its Aliso Canyon storage facility.
Photograph: Richard Vogel/AP

The utility company whose blown-out natural gas well forced the evacuation of thousands of people in the Los Angeles area faced criminal charges on Tuesday for failing to report the massive breach to the authorities.

With the criminal complaint, Southern California Gas Company faces mounting legal challenges for its response to the underground blow-out of its natural gas storage well, which was discovered on 23 October.

Earlier on Tuesday, the state of California joined a lawsuit against the firm.

In the criminal proceedings, SoCalGas was charged with failing to inform the authorities immediately upon discovering the blow-out at Aliso Canyon storage facility, and for spewing contaminants into the air.

The blow-out in one of the country’s largest natural gas storage wells was the largest known to experts, and is currently the single largest source of climate change pollution in California.

The breach, and the stench from the chemical added to the gas, forced schools to close and more than 4,400 people to flee their homes for temporary housing.

Under the charges, the company faces a maximum penalty of $25,000 a day for each of the three days it failed to report the breach to the emergency services, and up to $1,000 a day on the air pollution charges until the well is plugged.

Jackie Lacey, the LA county district attorney, acknowledged that the potential penalties would seem light to the thousands of residents of Porter Ranch who were forced to flee the upscale area after they were sickened by fumes.

“While we recognize that neither the criminal charges nor the civil lawsuits will offer the residents of Los Angeles County a complete solution, it is important that Southern California Gas Co be held responsible for its criminal actions,” Lacey said in a statement. “I believe we can best serve our community using the sanctions available through a criminal conviction to prevent similar public health threats in the future.”

The company came under additional legal pressure on Tuesday after Kamala Harris, California’s attorney general, joined a lawsuit filed by the city and county of Los Angeles accusing SoCalGas of breaking health and safety laws for failing to control the leak and report it to the authorities.

The lawsuit says that the breach has spewed 80,000 metric tons of methane into the atmosphere. Methane is a a far-more powerful climate pollutant than carbon dioxide in the short term, and the lawsuit contends that the breach will jeopardize California’s efforts to cut greenhouse gas emissions.

“The impact of this unprecedented gas leak is devastating to families in our state, our environment and our efforts to combat global warming,’’ Harris said. “This gas leak has caused significant damage to the Porter Ranch community as well as our statewide efforts to reduce greenhouse gas emissions and slow the impacts of climate change.”

There was no immediate response from SoCalGas to the criminal charges. The company is a subsidiary of Sempra Energy, the country’s largest natural gas distribution company, according to the company website.

The company has claimed the leak poses no threat to public health, but the strong smell from the chemical added to the gas to aid in leak detection has caused widespread nausea and headaches.

But a number of public health experts have raised concerns about the release of known toxins.

After several failed efforts to plug the leak, the company is now in the process of drilling a relief well. However, that process of drilling 8,000ft to intersect with a pipe that is seven inches in diameter – without hitting another pipe and springing another leak – is immensely complicated.